The present invention relates to an attachment stem for bicycle handlebars of the type comprising a shank, which can be coupled to the head tube of the front fork of the bicycle, and an arm which extends from the top of the shank and has a free end formed into an eyelet, the eyelet having a slit which divides it into a main jaw, which forms part of the arm proper, and an auxiliary sprung jaw, and in which a threaded blind hole is formed in the main jaw whilst a through-hole is formed in the auxiliary jaw in alignment with the blind hole for engagement by a screw for clamping the central part of the crossbar of the handlebars which is inserted in the eyelet.
Stems of this type are used particularly for racing handlebars. Their purpose is to provide the region of the joint between the stem and the crossbar of the handlebars with a shape which is both aerodynamic and aesthetic. In most conventional stems, it is necessary for the eyelet to be enlarged with a suitable tool which is inserted in the slit so as to lever the two jaws apart and allow the crossbar to slide in the eyelet for its assembly and removal. In the absence of a levering tool, a screwdriver or other bladed tool may be used for the same purpose. The Applicant's Italian utility model No. 194553 describes a stem of the type indicated which can be enlarged by means incorporated in the stem itself. More specifically, a threaded hole is formed in the auxiliary jaw of the stem substantially parallel to and alongside the through-hole (which has smooth walls and is of larger diameter than the screw) and an externally-operable pressure screw is engaged therein for reacting against the main jaw in order to enlarge the eyelet by forcing the jaws apart when the clamping screw is slackened.